Charlie Day isn't exactly the first name that springs to mind when asked, "Who should be one of the stars of Guillermo del Toro's new robots-versus-monsters movie?" Then again, who does spring to mind? In "Pacific Rim" -- footage of which Del Toro brought to Comic-Con where it received an enthusiastic response -- monsters are unleashed from below the ocean floor. To combat these monsters (or kaiju), giant, human-piloted robots are created. (Just writing that last sentence, good lord.)

I met Day at his hotel, away from the rambunctious Comic-Con crowd. Day is known for his bombastic on-screen persona (in films like "Horrible Bosses" and the TV series "It's Always Sunny In Philadelphia"), but the actor I met was extremely polite and genuinely excited to be in a movie about giant monsters and robots that fight. Here, Day explains what it was like to be on the set of "Pacific Rim," why he and Jason Sudeikis make such a great comedy team, and recounts his first acting gig -- which was opposite Mary Tyler Moore, of all people.

The "Pacific Rim" footage went over very well.
Did you get a chance to see it? It really is amazing. He's found a way to shoot in a different style. You know, this CGI kind of stuff, where he built so many practical things.

So a lot of this stuff we're seeing is actually there?
I rarely saw any green screen when I was filming.

That's really surprising. That's rare, these days.
Yeah. I knew at some point, there was going to be a giant monster drawn into the scene, but they were shaking the ground and flipping cars over around me. So everything was real.

Was that frightening? There's cars flipping over near you. You know, you see it in movies all the time. But that's really not a normal thing to be going on right next to you.
A little bit, yeah. And it was definitely the first time on a movie set where I felt like, "I could die here." I did get minorly electrocuted, but I didn't tell anybody.

Electrocuted?
You know, I wear this electric contraption on my head in some of the scenes and there was one day where I just kept getting this pinching in my ear, and then my cast mate, Burn Gorman, put it on, and he said, "I believe that's electric shocks." And it was a very sort of crudely made prop -- the idea was that my character had whipped it up very crudely and quickly, so it was supposed to look like that. But in its crudeness, I think there were mis-wires in there.

Did you hear the concept -- monsters versus robots -- and say, "I've got to be in this?"
Yeah. I mean, it's the kind of thing that I actually always really wanted to do. And I just assumed I would never get the opportunity to do it unless I had, you know, 10 or 15 films under my belt and someone said -- you know, like Adam Sandler in "Punch-Drunk Love" -- you know, someone thinks of you in a different light. Fortunately, Guillermo was a huge "It's Always Sunny in Philadelphia" fan and he just thought I was right for the character and I thought I was right for the character -- and so it's a happy marriage.

Is there comic relief with your character?
I mean, I think a little bit.

Because that can get tricky. No one wants to be in that "Rob Schneider in 'Judge Dredd'" area.
No, you don't. I mean, I think I look funny and sound funny, so people will want to laugh at me. I just heard this interesting interview with Mel Brooks where he was saying Gene Wilder would always get so upset because people would always laugh at him even when he was trying to be serious.

That's a good example. Because, I mean, just thinking of him right now, I just want to laugh. "I said good day!" Sorry, I've got to laugh.
Yeah, you just want to smile. So yeah, there is some of it ... and then he's won you over. So I think, yeah, there's definitely some levity that I bring to a dark film. But then I go through a harrowing experience and hopefully it becomes very unfunny and real and frightening after a point.

On set, was there ever a moment when you thought, Well, that's something I've never seen before.
This isn't new, but just to brag on Guillermo a little bit. There was a scene where my character's glasses get knocked off and I'm scrambling through the mud to try and find them. And he had built a pair of glasses that were, you know, you can't really see here, but maybe a yardstick long. And he built a giant pair of glasses that I'm trying to act as if I can't find. You know, and these things are bigger than half of me. And I knew when we were doing that -- I mean, I knew before -- but that I was in the hands of someone who visually was ... because, then, you see the shot, and the glasses are big in the frame and I'm big in the frame, and it's just a beautiful shot. They look like normal glasses. It's an Alfred Hitchcock move. So he was constantly doing things that you knew you were working with a special filmmaker.

My favorite current comedy duo is becoming Charlie Day and Jason Sudeikis.
Look, I love that guy to death. And for some reason, I think we just really respect each other and have maybe a very similar sense of what we find funny. And I've absolutely loved working with him in everything that we've worked in. And even when I did "Saturday Night Live"...

The "Seinfeld Crime Scene" sketch.
The "Seinfeld" sketch, which he'd written and he'd been trying to get on the show for years.

Why would no one put that on the show? That's amazing.
You know, I don't know. And we read it together and I played the cop and he played the detective. And then I said to him, "You know, it's good, let's try switching." And then somehow, we switched and it clicked. And you know, it was just great. I really hope that I can do many, many movies with that guy. I mean, he's really one of my favorite guys to work with.

Was there anything that you loved that was cut in dress rehearsal?
Well, I wish that the "Seinfeld" sketch aired earlier.

It was late in the show.
It was pretty late in the show.

And it was one of my favorite things in that show.
It was my favorite thing, too. But, look, I was so happy to be there that I was really just -- it's their show. It's a cast show.

You hosted one of the best episodes of the season.
Well, I appreciate that. I think a good host just kind of has a lot of fun and tries to fit seamlessly in and not sort of take the place over. And so I really was just -- whatever they wanted to do, I was game for it. And it was just the greatest experience. And a lot of those people are my peers. I've known Sudeikis now for a while and I've known Kristen Wiig since before she was on "SNL." And a lot of them are my age, so it was the right time. I think if it had happened to me when I was 23 years old or something, I would be in over my head. But it was just a wonderful experience. I hope I can do it again one day.

Will there be a "Horrible Bosses 2"?
We're waiting for them to call. I know that they want to make it and I know that they've written it. And as soon as they gives us a call and make us an offer, then we can start talking about it. But I think there will be.

You were in the "Mary and Rhoda" television reunion movie.
[Laughs] Yeah.

That was one of your first gigs, right?
It was, yeah.

What was that like? I mean, those are iconic characters.
I played the mailroom kid. I think I had one line and it's when Mary Tyler Moore walks into the office and checks her hair -- her reflection on a shiny wall or something. And my character oversees her doing it and says, "Lookin' fine," and keeps on walking. And when I auditioned, I did it somewhat sarcastically with the intention of, "Hey, you know, you don't have to ... you look fine. Don't worry about it." But when I shot it, the director's like, "Really make sure you're letting her know she looks good." And I was like, Oh, right, of course that's what they want.

They don't want to tell Mary Tyler Moore that she's not looking fine.
No, they don't want sarcasm here. And, yeah, so that was one of the first things I shot in New York. That was '99 or 2000.

[Day's appearance starts at 1:50 in the clip below.]

I know you've been in Comic-Con before. Do you get to walk around the floor?
Yeah, you know, there's a lot of "It's Always Sunny in Philadelphia" fans here. And we've been coming with the show for the last ‑‑ we didn't come this year, because we don't have an episode ready. But we come a lot and it's just so fun. These audiences, there's nothing lazy about these audiences. You know, they know your characters, they know your episodes. This movie hasn't even come out -- and it's completely secretive -- and people seem to know more about it than I do. And I was in it! You know? So it's really great to be with those people and bring them what they want.

Well, I hope that the Sudeikis/Day team continues. Or is it the Day/Sudeikis team? I don't know, which one should go first?
He can go first. That's fine. I really hope we do. I know we'll probably, hopefully, do "Horrible Bosses" again, but I really want to do other things with him. He's really my favorite guy to work with.

Mike Ryan is senior entertainment writer for The Huffington Post. You can contact him directly on Twitter.